This invention relates to a pump assembly for use in a pressurised water supply system. The invention further relates to a pressurised water supply system including such a pump assembly.
A known pump-operated water supply system is described in U.S. Pat. No. 5,464,327A. This is intended to maintain pressure in a system at all times following switching on the pump for the first time, and to ensure this result, the pump initially runs for 90 seconds, and thereafter always for a minimum period of 10 seconds. The consumption of electricity and water is not therefore an issue.
By contrast, it is sometimes necessary for a building or other construction site or a remote location to be provided with a fresh water supply system which draws water from a local tank when water is required, the tank being replenished on an occasional basis from some other source. Typically the system employs a pump, powered by a low-voltage electric motor, to draw water from the tank and supply that water under pressure to a tap mounted adjacent a basin provided at some suitable location. An instant heater, powered by bottled gas, may be fitted into the pipe from the pump to the tap, so that the system can deliver hot water. A pressure-sensitive switch is connected into the pipe from the pump to the tap, unless such a switch forms a part of the pump assembly itself, and controls operation of the motor driving the pump. When water is to be drawn, the tap is opened, the pressure in the pipe between the pump and the tap falls so closing the pressure sensitive switch, and current then flows from a battery to the pump motor. Frequently, an accumulator is connected to the pipe between the pump and the tap, in order to smooth out pressure variations and ensure that water is delivered immediately on opening the tap, without having to wait for the pump to start operating. Such an accumulator also allows a small quantity of water to be drawn without the pump starting, each time.
A water supply system as defined above is well-known and very widely used, not only on building and construction sites but also in caravans, motor-homes, boats and so on. It does however have the problem that if there are leakagesxe2x80x94and even very minor leakagesxe2x80x94downstream of the pump, the pressure in the pipe between the pump and the tap will gradually fall over a period time, and typically hours or even days. The pump will then be caused to operate, even when no water is to be drawn from the tap. This gives rise to a number of disadvantages, as follows:
a) The pump may operate at an unexpected time, such as in the middle of the night. Many designs of low voltage electric motor-driven pumps are somewhat noisy and if the system is installed for example in a caravan, motor-home or boat, the noise easily could wake up persons sleeping.
b) The operation of the pump when not required may impose a considerable and unnecessary drain on the battery powering the pump, so leading to the need to recharge the battery more frequently than otherwise would be required.
c) The tank can hold only a limited quantity of water and over an extended period of time, a minor leakage could amount to a significant proportion of the total held volume. The rate at which water will leak will be dependent upon the pressure in the system downstream of the pump and unnecessary operation of the pump maintains that pressure at a higher value than otherwise would be the case, leading to greater water losses.
The present invention aims at addressing the above problems associated with the known form of pressurised water supply system as described above.
According to the present invention, there is provided a pressurised water supply system for use in a location having no mains water supply, which supply system comprises a water tank, a water outlet tap, a water pump assembly installed in said water pipe and including a low-voltage dc pump motor, a water pipe connecting the tank to the tap, a pressure sensitive switch arranged to monitor the water pressure in the pipe between the pump and the tap and arranged to operate the pump when the switch detects a pressure below a pre-set low value, characterised in that there is provided a manually-triggerable timer disposed adjacent the tap and which timer inhibits operation of the pump despite the pressure sensitive switch detecting low water pressure below said pre-set low value other than during a timed period following manual triggering of the timer.
It will be appreciated that when a pressurised water supply system of this invention is used at, for example, a building or construction site; the interval between recharging a battery dedicated to supplying power to the motor of the pump may be extended by some months. Moreover, water consumption through leakage also is reduced, leading to the need to refill the water tank less frequently.
If the system is to deliver hot water, an instant water heater, powered by bottled gas, may be fitted into the pipe extending between the pump and the tap. In this case a branch pipe upstream of the heater may supply water to a cold tap.
In a preferred form of this invention, the pump comprises a low-voltage dc motor drivingly coupled to a water pump of a known design, such as a diaphragm pump or a centrifugal pump. Typically, the dc motor will be a 12 volt motor, for powering by a conventional 12 volt battery such as a lead-acid accumulator.
The timer which inhibits pump operation could operate on a number of different bases. For example a purely electronic timer could be employed, energised by depressing a switch, and which turns itself off at the end of a pre-set period. In a preferred embodiment, the timer includes a switch for connection in series with the power supply to the electrical pump, and a mechanical timer is coupled to the switch. Such a mechanical timer may comprise a spring-loaded pneumatic dash-pot coupled to a normally-open electrical switch, which switch is closed on depression of the dash-pot against the spring loading. Then, as the dash-pot is driven back to its initial position by the spring loading, the electrical switch will be opened once more so inhibiting pump operation. Rather than a piston and cylinder dash-pot, a flexing diaphragm arrangement may be employed. In either arrangement, the timer preferably is mounted closely adjacent the tap of the overall system, so that before water can be drawn from the tank, the timer must be operated so enabling the pump. If water had been drawn relatively recently, water flow may be expected more or less immediately, whereas if no water had been drawn for some time, then the pressure between the pump and the tap may have fallen such that pump operation must be re-started, before water will flow out of the tap.
In the pressurised water supply system of this invention, an accumulator may be connected to the pipe between the pump and the tap, to smooth out pressure variations, as with known water supply systems of this kind. On the other hand, such an accumulator will increase water wastage in the event that there is a small leak, and so it is preferred that the volume of the accumulator is minimised or that no accumulator at all is provided.
Means may be provided for re-charging a battery associated with the pump. Conveniently, the recharging means may be a solar cell array, able to deliver current to the battery during bright periods.
By way of example only, one specific embodiment of this invention will now be described in detail, reference being made to the accompanying drawing which diagrammatically shows a complete pressurised water supply system arranged in accordance with the invention.